In North America or Europe, there is a tendency that brown skin, which has been healthily tanned, is preferred. However, there is a concern that a suntan resulting from sunbathing or a tanning machine can cause cutaneous cancer or freckles by the effect of ultraviolet rays. Thus, a self-tanning agent is favorably used, which is capable of rendering the color of the skin a natural and healthy brown color similar to the color based on a suntan, without being affected by ultraviolet rays.
The self-tanning agent is also referred to as a sunless tanning agent, and is a skin cosmetic for coloring the skin. In many cases, as a component thereof for turning the skin into a brown color, dihydroxyacetone (DHA) is used alone, or is used together with erythrulose or some other components. When dihydroxyacetone is used together with erythrulose, usually, dihydroxyacetone is mixed at a higher concentration than erythrulose. By effect of these components, the stratum corneum of the skin becomes colored brown. It is said that this coloring is generally advanced by a browning reaction, and is caused by the generation of a polymer having a structure similar to that of a brown colorant called melanoidin. However, details of the reaction mechanism thereof have hardly been elucidated. For reference, in the field of food chemistry, a browning reaction is also called Maillard reaction. The browning reaction generally means a reaction through which a nitrogen-containing compound, such as an amino acid or a protein, and a reducing sugar are polymerized to generate melanoidin.
Sometimes, when a self-tanning agent is used, a distinct unpleasant odor is generated, and this causes a problem. Hitherto, however, little research and few reports have been made about unpleasant odors generated when this self-tanning agent is used. Thus, improvement of the technique is desired.
D. M. Hindenlang and M. E. McDonnell, Cosmetics & Toiletries magazine, 2008, Vol. 123, No. 7, p. 67-74, states that it is difficult to mask the odor generated when a self-tanning agent is used. However, this document does not have a description about the causative substance of the odor.
In the field of food, research has been made about the Maillard reaction, which is generated by a reducing sugar and an amino acid. H. E. Nursten, Food Chemistry, 1981, 6(3), 263-277, states that through a Maillard reaction between a dicarbonyl compound and an amino acid, a pyrazine compound is generated. However, the document does not have a description about a relationship between the pyrazine compound and any self-tanning agent. S. Fors, Sensory Properties of Volatile Maillard Reaction Products and Related Compounds, “The Maillard Reaction in Foods and Nutrition” (ACS Symposium Series, Vol. 215), Chapter 12, pp. 185-286 Publication Date (Print): Apr. 29, 1983, describes odors obtained by Maillard reaction in the field of food chemistry. In this document, it is stated that a pyrazine compound emits a pleasant odor by which a food is characterized. For example, 2,6-dimethylpyrazine has a “sweet, fried, resembling fried potatoes, nutty, and roasted” odor. However, this document does not refer to a relationship between the pyrazine compound and a self-tanning agent.
As described above, a sufficient investigation has not yet been made about compounds generated by a reaction between a self-tanning agent and the skin. Moreover, volatile components known as a product from Maillard reaction in the field of food have been recognized as favorable and pleasant odor components, and been conceived to be irrelevant to the unpleasant odor generated by a reaction between a self-tanning agent and the skin.